JP5885964B2 - Stand-off explosive detector using deep UV Raman spectroscopy - Google Patents

Description

  This application claims the benefit of US Provisional Application No. 61 / 374,465, filed Aug. 17, 2010. The provisional application is incorporated herein by reference in its entirety.

(Field of the Invention)
The present invention relates to Raman spectroscopy, and more particularly to a system and method for performing stand-off Raman spectroscopy using laser light in the deep ultraviolet spectral region.

(Background of the present invention)
The risk of exposure to chemical or biological factors can be serious. For example, quickly and accurately identifying (1) the type of agent released and (2) the exact area of contamination, whether as a result of an unintentional release due to an accident or the result of deliberate delivery Is desirable. Such rapid and accurate detection of dangerous substances can be an important factor in reducing possible injuries and limiting further diffusion of factors such as by wind, human and animal contact.

  Similarly, it is important to be able to quickly and accurately identify explosive materials. Such detection is particularly important in security and military environments. The earlier detection can take place, the faster staff can be evacuated or other appropriate measures can be taken.

  Designed to measure surface-deposited chemical contamination, traditional remote sensor technology uses vehicles and associated test equipment to recover the physical sample of the contamination, and then extremely cumbersome to analyze the sample And using a mechanical sampling wheel system coupled to a time consuming process, for example a mass spectrometer for testing against chemical factors.

  In view of the complexity of such an approach, a newer and simpler technology was desired. One emerging technology that responds to this desire is commonly referred to as “stand-off surface detection,” a category of technology that enables the detection of substances without the need to actually make physical contact with the substance. Point to. The goal of these detection systems is to (contain) further contamination by providing the ability to detect, identify, locate, quantify, alert, and report chemical and biological threats. To warn military units or civilian personnel early enough to avoid and deploy appropriate counter-attack measures.

  One of the technologies that enables standoff surface detection is Raman spectroscopy. Raman spectroscopy is used to characterize materials and then identify such materials. Laser transmitters typically serve as spectrally narrow light sources with high irradiance. Lasers irradiate, among other things, known or unknown substances such as chemical compounds, biological agents, or explosive materials. A portion of the incident light is Raman scattered by the material. This light is not only scattered in all spatial directions, but is also spectrally shifted to discrete wavelengths. These wavelength shifts correspond to the natural vibrational energy associated with the molecular bonds of the material.

  In conventional stand-off Raman spectroscopy systems, Raman scattered light is collected by a telescope and coupled into a dispersive optical system. The telescope collects the collected light, for example, on an optical fiber bundle. At the opposite end of the fiber bundle, individual fibers are oriented linearly to form an entrance slit for the grating-based spectrograph. The electro-optic detector array records the optical spectrum of the Raman scattered light. This spectrum serves as a “fingerprint” of known or unknown material. The analysis computer adds information identifying known substances, stores reference spectral information, and identifies unknown substances from large, low, pre-analyzed and "fingerprinted" spectral libraries of reference substances Use a pattern matching algorithm.

  Laboratory-based Raman spectroscopy systems have been used for many years. Recently, portable Raman systems have become possible as a result of reduced size parts and inherent embedded technology. A description of one such portable system can be found in US Pat. Human portable Raman sensors implemented in backpacks have also recently been put to practical use by ITT (Wilmington, DE). Aspects of the system are described in Patent Document 2 entitled “Method, Apparatus and System for Rapid and Sensitive Standoff Detection of Surface Continants”, which is also incorporated herein by reference. Truck-mounted Raman sensors have also been used in practice to date. For further discussion of the Raman spectrum measurement method, reference can also be made to Patent Document 3, which is incorporated herein by reference.

US Pat. No. 6,608,677 US Pat. No. 7,796,251 US Pat. No. 6,788,407

  Despite these known systems, we provide different forms of Raman sensors specifically to meet the needs of both civilian and military personnel responsible for identifying trace or residual explosive materials Needs to remain.

(Summary of Embodiments of the Invention)
The present invention provides a unique implementation of a Raman spectroscopy system that can be used to avoid the need to be in close proximity to dangerous substances or items. More specifically, embodiments in accordance with the present invention allow personnel to use explosive materials (eg, TNT and RDX), homemade explosives and their precursors, and chemical weapons (CWA) and toxic industrial chemical factors. Remote, including inspection of buildings, equipment, vehicles, aircraft, and other artificial or natural surfaces for the presence of unknown substances or items, including but not limited to (TIC) Provided the ability to use sensitive sites. One of the significant advantages of embodiments of the present invention is that there is no need to place personnel in locations where explosives can be concealed, searching for explosive explosive devices (IEDs) or small amounts of explosives on a vehicle, And the ability to detect.

  Other advantages of embodiments of the present invention are that the technology is (1) a non-contact standoff system, (2) allows mapping of surface contamination, and (3) provides a quick response (typically detection) For providing only a few seconds).

  These and other features of the embodiments of the present invention and their attendant advantages will be more fully appreciated upon reading the following detailed description of the associated drawings.

For example, the present invention provides the following items.
(Item 1)
A method of performing Raman spectroscopy, the method comprising:
Using a laser beam to irradiate a very small amount of target substance placed on the painted surface;
Receiving the laser light and the Raman return signal reflected from the trace amount of the target substance;
Processing the Raman return signal using at least a spectrograph and a camera to obtain a Raman signature for the target substance;
Identifying the target substance based on the Raman signature for the target substance and a database of Raman signatures;
The method wherein the ratio of the Raman return signal power to the fluorescence power is at least about 0.1.
(Item 2)
A method according to any of the preceding items, wherein the ratio of the power to fluorescence power of the Raman return signal is between 0.1 and 0.5.
(Item 3)
A method according to any of the preceding items, wherein the ratio of the power to fluorescence power of the Raman return signal is greater than 0.5.
(Item 4)
A method according to any of the preceding items, wherein the target substance is located on a vehicle panel.
(Item 5)
The method of any of the preceding items, wherein the laser light has a wavelength of about 248 nm.
(Item 6)
The method according to any of the preceding items, wherein the target substance comprises a balance of explosive material having a concentration of about 100 μg / cm ² or less.
(Item 7)
The method according to any of the preceding items, wherein the target substance comprises a balance of explosive material having a concentration of about 50 μg / cm ² or less.
(Item 8)
The method according to any of the preceding items, wherein the target substance comprises a balance of explosive material at a concentration of about 5 μg / cm ² or less.
(Item 9)
The method according to any of the preceding items, wherein the power of the laser light is about 100 mW.
(Item 10)
The method according to any of the preceding items, wherein the Raman return signal is detected from a stand-off distance of at least 10 meters and the target substance is 45 μg or less of PETN.
(Item 11)
The method according to any of the preceding items, wherein the Raman return signal is detected from a stand-off distance of at least 10 meters and the target substance is 5 μg or less of RDX.
(Item 12)
The method according to any of the preceding items, wherein the Raman return signal is detected from a standoff distance of at least 10 meters and the target substance is an AN of 500 ng or less.
(Item 13)
Using a laser beam to irradiate a very small amount of target substance placed on the painted surface;
Receiving the laser light and the Raman return signal reflected from the trace amount of the target substance;
Processing the Raman return signal using at least a spectrograph and a camera to obtain a Raman signature for the target substance,
The method wherein the wavelength of the laser light is 248 nm and the ratio of power of the Raman return signal to fluorescence power is at least about 0.2.
(Item 14)
A method according to any of the preceding items, wherein the target substance is disposed on a vehicle panel.
(Item 15)
The method according to any of the preceding items, wherein the power of the laser light is about 100 mW.
(Item 16)
The method according to any one of the above items, wherein a standoff distance between the laser emitting the laser light and the target substance is about 10 meters.
(Item 17)
The method according to any one of the above items, wherein the target substance is 45 μg or less of PETN.
(Item 18)
A laser that generates laser light at a wavelength of 248 nm;
A telescope configured to receive a Raman return signal from a trace amount of a target substance excited by the laser light;
A spectrograph configured to disperse the Raman return signal received via the telescope to a constituent wavelength of the Raman return signal and generate a corresponding optical signal;
An apparatus in communication with the spectrograph and configured to convert the optical signal output from the spectrograph to an electrical signal,
A device wherein the ratio of power of the Raman return signal to fluorescence power is at least about 0.1 when the device is in use.
(Item 19)
Any of the preceding items, further comprising an analysis computer configured to compare the electrical signal with each of the Raman signatures stored in the library and to identify the target substance. The device described in 1.
(Item 20)
The apparatus according to any of the preceding items, wherein the power of the laser light is about 100 mW.

(Summary)
Method of performing Raman spectroscopy, and using a laser beam to irradiate a trace amount of a target substance placed on a painted surface, and receiving a laser beam and a Raman return signal reflected from the trace quantity of the target substance Processing a Raman return signal using at least a spectrograph and a camera to obtain a Raman signature for the target substance, and identifying the target substance based on the Raman signature for the target substance and a database of Raman signatures An apparatus for performing the method. The wavelength of the laser light can be selected based on the ratio of the Raman return signal power to the fluorescence power.

FIG. 1 is a schematic functional diagram of a Raman spectroscopy system according to an embodiment of the present invention. FIG. 2 depicts a plot of Raman photon efficiency factors including three identified resonance regions. FIGS. 3A-C depict plots of fluorescence spectra recorded from vehicle panels used in connection with experiments conducted in accordance with embodiments of the present invention. FIG. 4A shows Raman to fluorescence power ratio data for the explosive material PETN. FIG. 4B shows Raman to fluorescence power ratio data for the explosive substance Semtex. 5A and 5B depict a plot of the spectrum of a selected vehicle panel used in connection with experiments conducted in accordance with embodiments of the present invention. FIG. 6A depicts a plot of Raman shift versus PETN using 248 nanometer excitation with a 10 meter standoff. FIG. 6B depicts a plot of Raman shift versus TNT using 248 nanometer excitation with a 10 meter standoff. FIG. 7A depicts a plot of Raman shift against the remainder of AN on an aluminum coated glass in connection with a method according to an embodiment of the present invention. FIG. 7B depicts a plot of Raman shift against the remainder of the AN on the surface of the vehicle panel in connection with a method according to an embodiment of the invention.

  Raman signatures tend to be unique and unique to the material, so this “optical fingerprint” technique for identifying explosives at standoff distance has received much attention. Raman signals can be generated using laser excitation, and many studies have been conducted to evaluate Raman spectroscopy for detection of explosives in the near infrared, visible, and UV spectral regions. This flexibility encourages the development of Raman systems and allows some Raman systems to detect explosives from tens of meters.

  In this regard, many academic studies concentrate on only one aspect of Raman spectroscopy for the detection of explosives, demonstrating the feasibility of long standoff distances or the potential of certain dual sensor concepts. To do. In general, these studies are conducted under experimental conditions that are not particularly similar to real-world real-world behavior. For example, Petersson, A. et al. Wallin, S .; Oestmark, H .; Ehlerding, A .; Johansson, I .; Nordberg, M .; Ellis, H .; Al-Khalili, A .; Proc. Although the study shown in OF SPIE, 2010, 7664, 76641K-1 proves that ammonium nitrate (AN) can be detected from a distance of 470 meters outdoors using a 532 nm Raman system, the data is basically Recorded using laboratory conditions. Specifically, a bulk AN 500 mL container was investigated for a period of 1-10 seconds using 320 mJ pulse energy (ie, about 3.2 watts of laser power) at a repetition rate of 10 Hz.

Increasing the distance and detecting many types of explosives at very low concentrations continues to be an area of interest. Being described herein, the 10 meter standoff distance using moderate laser power (about 100 milliwatts), a low concentration as ^{3μg / cm 2 ~50μg / cm 2} , TNT, PETN, and It is a UV Raman sensor shown to detect AN. Significantly, this level of sensitivity is proven against the backdrop of explosives on the ground in relation to the field in a time frame on the order of a few seconds. The above is a key point because real world backgrounds such as the painted surface of a vehicle panel often limit the sensitivity of Raman spectroscopy by overwhelming the Raman signal with fluorescence. Furthermore, the choice of excitation wavelength is related to the amount of material present.

  Detecting some explosives can be particularly difficult because Raman scattering from these materials is insufficient to overcome the limitations imposed by absorption. In general, strong absorption limits the penetration of the target by the incident laser beam and minimizes the volume of material that can contribute to the Raman signal. Emerging Raman signals are also absorbed by the target along the path to the receiver. As a result, the amount of material that can contribute to the Raman signal is limited to a thin layer against strongly absorbing explosives. RDX and HMX absorb strongly between 225 nm and 275 nm, and the thickness of the material contributing to the signal is expected to be less than 0.3 μm (for 257 nm excitation). Ultimately, the signal strength depends not only on absorption but also on the efficiency of Raman scattering. For example, the Raman scattering from TNT is about 100 times stronger than the Raman scattering from RDX using 257 nm excitation, so that the absorption limits the theoretical interaction depth for TNT to about 100 nm. The Raman signal obtained from TNT is much larger than the Raman signal obtained from RDX.

Embodiments of the present invention use deep UV lasers to generate Raman scattering from surface chemical factors. Raman scattering is generally much stronger with UV laser light than visible and infrared light due to the occurrence of the phenomenon known as the well-known ν ⁴ effect and resonance increase. Importantly, unlike the Raman signals obtained using visible and infrared lasers, the resonance increase tends to emphasize the spectral features of the target explosive when compared to the spectral features obtained from the background, Makes it possible to detect small amounts of explosives. In addition, the system is a solar blind and there is minimal interference from background fluorescence. Single frequency lasers can be used and the processing does not require registration between pictures, which is required for differential imaging techniques.

FIG. 1 depicts a Raman spectroscopy system according to one possible implementation of the present invention. The scanner 170 is a UV laser tuned to a single frequency in the wavelength region of less than 400 nm, preferably less than 250 nm, more preferably about 248 nm to avoid fluorescence from the relevant surface, as will be discussed in more detail below. 10 is included. The outgoing UV beam of the laser is allowed to radiate to the target material via the safety shutter 20 and the beam conditioning optics 30. The beam adjustment optical system 30 adjusts the characteristics of the beam so as to match the survey spot size of the receiver telescope 70. This beam radiates from the system to a surface where a trace amount of an unknown chemical agent, such as an explosive material or precursor, is volumed. As used herein, the phrase “trace” is meant to refer to the remainder of a substance, a specimen, etc., and to be distinguished from a bulk material. The trace amount can be, for example, about 100 μg / cm ² .

  UV laser light interacts with the target surface and the deposited chemicals on the surface. The return light consists of Rayleigh scattered light and Raman scattered light from the surface and target chemical factors. In parallel with the UV laser, the distance meter 40 detects the range from the system to the surface of the investigation. Data from the rangefinder 40 can be used by the control electronics 50 to control the beam conditioning optics 30 and to control the focusing of the telescope 70 received via the autofocus control module 60.

  Telescope 70 receives Rayleigh and Raman scattered light and focuses it on optical filtering and beam shaping or conditioning module 80. The optical filtering portion filters Rayleigh scattering (basic UV laser light) and collects the resulting filtered light onto the end of the fiber optic bundle 90. The near ends of the fiber optic bundle are arranged in a generally circular arrangement to maximize coupling. The far end, the end closest to the spectrograph 100, is preferably arranged with a linear array of individual fibers to create a slit. Depending on the specific design, the linear array can be arranged in a shallow v array to offset the optical effects that occur in the spectrograph 100. The spectrograph 100 uses gratings and optical components to disperse the received light at its constituent wavelengths and to focus the light onto a charge coupled device or other array detector (referred to as camera 110). The camera 110 can be a multiplying CCD (ICCD) to amplify the Raman return signal. The camera 110 converts the optical signal into an electronic waveform that represents the amplitude of light in each wavelength bin. This signal is then processed and compared against a library of signatures in analysis computer 120. The process uses the removal of any residual baselines from the received signal and the spectral response of the system in advance so that the measured signal and the library spectrum appear to be measured by the same system. Adjusting. When analysis computer 120 determines a match, the computer provides the operator with a visual, audible, and / or textual notification (indicated by reference numeral 130) indicating the presence, name, etc. of the detected material.

  The scene to be analyzed can be observed using video camera 140. The system illuminates the telescope field of observation with an indicator 150 indicating the survey area to the system operator. In some applications, the rangefinder 40 beam may be used as an indicator. The operator instructs the system to scan the area of interest using a scan control computer 160 that controls the entire scanner 170. The scan can be completed manually upon viewing the video scene, or the operator can specify the area on the video display that he wants to scan. Next, the scan control computer 160 calculates the scan paths of the UV laser 10 and the telescope 70. Scans can also be used as part of a mapping function to map an area of interest for the presence of one or more target substances.

  As will be appreciated by those skilled in the art, this system can be used to remotely probe surfaces for specific chemical factors including explosives and their precursors. Other chemical factors can also be detected if their spectra are included in the active library used by the algorithm. In one possible implementation, the system may be deployed on a mobile or mobile vehicle.

  An important aspect described herein is the selection of the wavelength of the laser light. Minimizing interference from real-world background fluorescence while avoiding sample degradation should be the primary driver for selecting the appropriate laser wavelength in systems that do not use more complex and faster gated detectors It is determined. Phenomenological research is undertaken to spectroscopically characterize explosives on a real-world background, including 32 vehicle panels, some of which are listed in the table below. As discussed in more detail below, laser excitation at 248 nanometers sufficiently minimizes fluorescence interference and sample degradation.

  The Raman response from several explosives was investigated using laser excitation between 225 and 275 nm. It is concluded that excitation near 257 nm can be well suited for detecting explosive residues for the following reasons.

  1) Preliminary data recorded from a small number of randomly selected vehicle panels shows that the fluorescence generated by laser excitation at wavelengths longer than 257 nm can greatly reduce the sensitivity to microexplosives.

  2) A simple prediction shows that the intensity of the Raman signal prefers a longer excitation wavelength and is maximum for any of the explosives tested at 257 nm.

  3) Samples that absorb strongly tend to produce Raman signatures that provide evidence for photodegradation when recorded using laser wavelengths shorter than 257 nm.

  These factors generally describe a “Raman photon efficiency factor” in which the Raman signal intensity is divided by the excitation wavelength. Although the Albrecht theory can predict the wavelength for the largest Raman cross section, this approximation merely does not incorporate the effects of reabsorption and light penetration into the sample into the Raman signal intensity. FIG. 2 is a plot of Raman photon efficiency factors that can be described in three regions.

• Non-resonant wavelength: ν ⁴ dependent dominance; small dispersion derived from molar extinction coefficient • Approaching or before resonance: abrupt increase in Raman scattering and a relatively smaller increase in molar extinction coefficient • High resonance, high extinction coefficient : A small increase in Raman scattering intensity relative to the molar extinction coefficient resulting in a high probability of photon / thermally induced change or degradation. When the excitation wavelength approaches resonance, the Raman signal intensity is increased, but more It is found that the balance is maintained by small photon-molecule interactions. As the excitation wavelength moves closer to the optimal resonance, the increase in Raman signal strength is further suppressed by very small photon-molecule interactions relative to the point where the signal strength competes with system noise / interference or efficiency. Although active / explosive materials can be classified in small sets of groups, each material has a unique Raman photon efficiency profile. Experiments to collect signal intensity versus laser wavelength data have been performed on a sample of the explosive material PETN where the excitation near 257 nm is 100 micrometers thick and the components UN and AN of the explosive material. (Theoretically) is close to the maximum signal possible. Similar data for the explosive materials TNT, RDX, and HNX show a lesser degree of change for the 100 micrometer sample, but the signal strength is always stronger at longer wavelengths.

  To obtain additional data, further studies compared explosive 257 nm Raman signals with spectra obtained from randomly selected vehicle panels to determine whether fluorescence severely limits sensitivity. To do. Some of the vehicle panels show overwhelming fluorescence with 257 nm illumination. Thus, three additional laser wavelengths (253 nm, 248 nm, and 244 nm) are also evaluated. Since the excitation wavelength is increased in small steps (Δλ = 4 nm or 5 nm), the Raman signal identifies the “Raman to fluorescence power ratio” that is optimal for the interference signal from the background and the Raman photon efficiency factor. It is possible.

  Shown in FIGS. 3A-3C are fluorescence spectra obtained from 17 randomly selected painted vehicle panels recorded using Ti: sapphire lasers operating at 257 nm, 253 nm, and 248 nm, respectively. It is. As can be appreciated, the intensity of the observed fluorescence is significantly reduced when the excitation wavelength is shifted from 257 nm to 248 nm. Importantly, research shows that the intensity of the Raman signal from the explosives of interest does not change dramatically with respect to the excitation wavelength. Therefore, the larger Raman to fluorescence power ratio at 248 nm excitation is important. This point is shown in FIGS. 4A and 4B, which show the Raman to fluorescence power ratio for PETN and Semtex (formulations containing PETN and RDX), respectively, processed on vehicles shown as background for explosive materials. Is understood by the data.

  Details of the vehicles used in the experiments described herein are:

including. The panel from the vehicle shown by Asterix is used in a separate experiment as discussed further below.

The power ratio of Raman to fluorescence in the waveband of interest is derived by calculating the absolute spectral difference over the 700-2000 wavenumber (cm ⁻¹ ) Raman signal waveband. Inclusion of the signature carbon-hydrogen bond (CH) region (waveband 2000-3000) can further reduce the value, but the main information used in detecting and identifying the explosive residue is: Note that a better system design method is created that is included in the waveband used.

Experiments, using an appropriate laser power (about 100 mW), showing the ability to detect TNT, PETN and AN from the stand-off distance 10 meters at low concentrations of about ^{3μg / cm 2 ~50μg / cm 2} . In particular, unambiguous detection is reported for samples containing PETN with a mass of about 45 μg, RDX with a mass of about 5 μg, and AN with a mass of about 500 ng.

  More specifically, vehicle panels # 5, # 15, # 31, and # 32 (see the table above) are randomly selected for testing with the deposited explosive residue. The spectra obtained from these panels are shown in FIGS. 5A and 5B. This set of Raman spectra quantitatively represents the four types of spectra observed. Note that the strength of the recorded signal from vehicle panel # 15 is found to be significantly stronger than those of the other vehicle panels. The spectrum of # 31 is vertically offset in FIG. 5B for clarity. The Raman band due to the surrounding nitrogen and oxygen is marked. The oxygen Raman band is not clear due to the overlap with the Raman band from each surface.

Shown in FIGS. 6A and 6B and FIGS. 7A and 7B are PETN (FIG. 6A), TNT (FIG. 6B), and TNT deposited on various surfaces with 248 nanometer excitation and 10 meter standoff. 7 is a spectrum obtained from the remainder of AN (FIGS. 7A and 7B). Each spectrum shown in FIGS. 6A and 6B corresponds to the average of 25 consecutive acquisitions (total integration time of 850 milliseconds), and those in FIGS. 7A and 7B correspond to the amount of change in the signal summation average. More specifically, FIG. 7A depicts the residual UV spectrum of AN on an aluminum-coated glass, and FIG. 7B shows a plot of vehicle surface # 31. The corresponding number of acquisitions (34 milliseconds for each number) is shown on the right hand side of FIG. 7B. The trace is offset vertically for clarity. The estimated surface concentrations of AN for FIGS. 7A and 7B are about 10 μg / cm ² and about 20 μg / cm ² , respectively, which are hardly detected by the eye.

  In all cases, it is possible to find a portion of the data set that produces a signal-to-noise ratio of greater than 10 for a significant band of AN with a total accumulation of less than 1 second (25 acquisitions).

  As noted, embodiments of the present invention use “deep UV” laser wavelengths, ie wavelengths below 250 nm. Fluorescence at 262 nm, although not impossible for all wavelengths from 250 nm to 1000 nm, makes detection of trace explosives difficult in the significant standoff range (greater than 5 meters). The use of the wavelength range is important. The Raman sensor described herein also has the ability to investigate more than a very small amount of bulk sample.

  As noted, detectable substances include explosive materials having a Raman signature, toxic chemical agents, biological and chemical weapons, and other materials.

  The systems and methods described herein may be embodied in other specific forms without departing from the spirit or basic characteristics of the specification. Therefore, the above embodiments are to be considered exemplary in all respects and are meant to be non-limiting.

10 UV Laser 20 Safety Shutter 30 Beam Adjustment Optics 40 Distance Meter 50 Control Electronics 60 Auto Focus Control Module 70 Receiver Telescope 80 Optical Filtering and Beam Shaping or Adjustment Module 90 Fiber Optic Bundle 100 Spectrograph 110 Camera 120 Analysis Computer 140 Video Camera 150 Indicator 160 Scan Control Computer 170 Scanner

Claims (20)

A method of performing Raman spectroscopy, the method comprising:
Using a laser beam to irradiate a very small amount of target substance placed on the painted surface;
Receiving the laser light and the Raman return signal reflected from the trace amount of the target substance;
Processing the Raman return signal using at least a spectrograph and a camera to obtain a Raman signature for the target substance;
Identifying the target substance based on the Raman signature for the target substance and a database of Raman signatures;
The ratio of power to the fluorescence power of said Raman return signal is also less 0. 1 der is, electric power versus fluorescence power the ratio of the Raman return signal is derived by calculating the absolute spectrum difference across the Raman signal wave band 700-2000 wave number (cm ^-1), and methods.   The method of claim 1, wherein the ratio of the power to fluorescence power of the Raman return signal is between 0.1 and 0.5.   The method of claim 1, wherein the ratio of the power to fluorescence power of the Raman return signal is greater than 0.5.   The method of claim 1, wherein the target material is located on a vehicle panel.   The method of claim 1, wherein the laser light has a wavelength of about 248 nm. The method of claim 1, wherein the target substance comprises a balance of explosive material having a concentration of about 100 μg / cm ² or less. The method of claim 1, wherein the target substance comprises a balance of explosive material having a concentration of about 50 μg / cm ² or less. The method of claim 1, wherein the target substance comprises a balance of explosive material having a concentration of about 5 μg / cm ² or less. Power of the laser beam is about 100 mW, the method according to claim 1. 10. The method of claim 9, wherein the Raman return signal is detected from a stand-off distance of at least 10 meters and the target material is PETN having a mass of 45 [mu ] g . 10. The method of claim 9, wherein the Raman return signal is detected from a standoff distance of at least 10 meters and the target material is RDX having a mass of 5 [mu ] g . 10. The method of claim 9, wherein the Raman return signal is detected from a standoff distance of at least 10 meters and the target material is AN having a mass of 500 ng. Using a laser beam to irradiate a very small amount of target substance placed on the painted surface;
Receiving the laser light and the Raman return signal reflected from the trace amount of the target substance;
Processing the Raman return signal using at least a spectrograph and a camera to obtain a Raman signature for the target substance,
0 the wavelength of the laser light is 248 nm, the ratio of power to the fluorescence power of said Raman return signal is also reduced. Are two der, said power vs. fluorescence power the ratio of the Raman return signal is derived by calculating the absolute spectrum difference across the Raman signal wave band 700-2000 wave number (cm ^-1), and methods.   The method of claim 13, wherein the target material is disposed on a vehicle panel. Power of the laser beam is about 100 mW, the method according to claim 13.   The method according to claim 13, wherein a standoff distance between the laser emitting the laser light and the target substance is about 10 meters. The method according to claim 16, wherein the target substance is PETN having a mass of 45 μg. A laser that generates laser light at a wavelength of 248 nm;
A telescope configured to receive a Raman return signal from a trace amount of a target substance excited by the laser light;
A spectrograph configured to disperse the Raman return signal received via the telescope to a constituent wavelength of the Raman return signal and generate a corresponding optical signal;
An apparatus in communication with the spectrograph and configured to convert the optical signal output from the spectrograph to an electrical signal,
When the device is in use, the ratio of power to the fluorescence power of said Raman return signal, at least Ri about 0.1 der, said power vs. fluorescence power the ratio of the Raman return signal, 700-2000 wavenumber An apparatus derived by calculating an absolute spectral difference over a (cm ⁻¹ ) Raman signal waveband .   19. The analysis computer of claim 18, further comprising an analysis computer configured to compare the electrical signal with each of the Raman signatures stored in a library and to identify the target substance. Equipment. Power of the laser beam is about 100 mW, according to claim 18.